So mayors announce at the Global Climate Action Summit in San Francisco. Emissions continue to fall. 66 cities expect to peak by 2020.

Wired: “That’s a big deal in the fight against climate change.” More than half the world’s population lives in cities – a proportion expected to grow.

Method: C40 compares a given city’s numbers year over year. To count as a peak, that high point in emissions must be at least 5 years ago, which avoids a false peak.

Image: screenshot from C40 website